feat: add notification sounds (#44)

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### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
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Reviewed-on: #44
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src-tauri/src/windows_toast.rs

@@ -0,0 +1,63 @@
+use tauri::command;
+
+#[cfg(target_os = "windows")]
+use windows::{
+    core::{HSTRING, Result as WindowsResult},
+    Data::Xml::Dom::*,
+    UI::Notifications::*,
+};
+
+#[cfg(target_os = "windows")]
+#[command]
+pub async fn send_windows_toast(title: String, body: String) -> Result<(), String> {
+    show_toast_notification(&title, &body)
+        .map_err(|e| format!("Failed to show toast notification: {}", e))
+}
+
+#[cfg(target_os = "windows")]
+fn show_toast_notification(title: &str, body: &str) -> WindowsResult<()> {
+    // Create the XML for the toast notification
+    let toast_xml = format!(
+        r#"<toast>
+            <visual>
+                <binding template="ToastGeneric">
+                    <text>{}</text>
+                    <text>{}</text>
+                </binding>
+            </visual>
+            <audio src="ms-winsoundevent:Notification.Default" />
+        </toast>"#,
+        escape_xml(title),
+        escape_xml(body)
+    );
+
+    let xml_doc = XmlDocument::new()?;
+    xml_doc.LoadXml(&HSTRING::from(toast_xml))?;
+
+    // Create the toast notification
+    let toast = ToastNotification::CreateToastNotification(&xml_doc)?;
+
+    // Create a toast notifier with an application ID
+    let notifier = ToastNotificationManager::CreateToastNotifierWithId(&HSTRING::from("Hikari Desktop"))?;
+
+    // Show the notification
+    notifier.Show(&toast)?;
+
+    Ok(())
+}
+
+#[cfg(target_os = "windows")]
+fn escape_xml(text: &str) -> String {
+    text.replace('&', "&amp;")
+        .replace('<', "&lt;")
+        .replace('>', "&gt;")
+        .replace('"', "&quot;")
+        .replace('\'', "&apos;")
+}
+
+// Stub for non-Windows platforms
+#[cfg(not(target_os = "windows"))]
+#[command]
+pub async fn send_windows_toast(_title: String, _body: String) -> Result<(), String> {
+    Err("Windows toast notifications are only available on Windows".to_string())
+}